Height-adjusting mechanisms of the aforesaid type, wherein the height of the chair seat is adjusted by rotation of the chair seat when unoccupied, with the adjusting mechanism being disengaged when the chair seat is occupied, are well known and such mechanisms are widely used on spindle-type office chairs. Examples of known height-adjusting mechanisms for chairs are disclosed in U.S. Pat. Nos. 4,324,382, 4,394,001, 4,026,509, 3,799,485, 3,164,357, 3,599,924, 3,727,871, 3,870,271, 3,991,965, 4,540,148, 4,494,721, 3,870,270, 4,379,540 and 2,702,075.
In a typical height-adjusting mechanism, such as illustrated in many of the above-identified patents, a spindle is threadably engaged with a nut which can be suitably held in nonrotatable relationship relative to either the base or the chair seat so as to define adjusting and nonadjusting positions. A spring normally urges the chair seat slightly upwardly when it is unoccupied so that the nut is clutchably connected to the base, whereby rotation of the seat causes the spindle to threadably move through the nut and hence cause a height adjustment of the seat. Conversely, when the chair seat is occupied, the external load imposed on the chair seat overcomes the spring and moves the chair seat and spindle downwardly a limited amount so that the nut is nonrotatably engaged with the spindle, whereby swiveling or rotating the occupied chair seat does not change its height.
While height-adjusting mechanisms of the aforementioned and similar types have performed in a generally satisfactory manner relative to their capability to permit deliberate adjustments in height, nevertheless it has been observed that many of these mechanisms permit undesirable height loss. More specifically, in many of the mechanisms it has been observed that when an occupant exits a chair, the chair is forcibly rotated through a part of a revolution due to the occupant rising and then walking away from the chair, during which movement the occupant effects a limited swiveling of the chair. In many of the known height-adjusting mechanisms, this limited swiveling is assisted in part by the weight of the chair and is sufficient to effectively cause an undesired amount of free-wheeling rotation of the chair seat so that the chair tends to unwind downwardly along the nut. Hence, each time the occupant departs the chair, a small height loss may occur and, while each height loss itself may be a very small vertical increment, nevertheless these increments gradually accumulate to a sufficient magnitude as to require the occupant to readjust the chair height.
In an attempt to overcome this problem, some height-adjusting mechanisms have attempted to incorporate an additional braking feature so as to prevent free-wheeling of the chair when the occupant leaves the chair.
For example, U.S. Pat. No. 4,379,540 discloses a screw-nut height-adjusting mechanism which additionally employs a split friction sleeve which coacts between the relatively rotatable spindle and screw for exerting a continuous frictional drag therebetween so as to prevent undesired relative rotation therebetween and hence undesired loss of height. The overall mechanism of this patent, however, possesses structural and functional relationships which are considered inadequate in order to provide a chair having desired load-carrying and reliability characteristics. This mechanism is further complicated by requiring a threaded adjustment shaft separate from the support spindle, and wear of the friction sleeve will probably be excessive so as to hence prevent the mechanism from providing satisfactory long-term operation.
British Patent Specification No. 647 183 and German Patentschrift No. 687 506 both disclose a nut threaded to a spindle and spring-urged axially to frictionally engage a support pedestal when the seat is unoccupied to permit height adjustment. The nut has or cooperates with a wedge-shaped split sleeve which is urged into frictional engagement with the threaded spindle when the seat is occupied. This latter relation creates an undesirable friction brake. Also, with the nut surrounding and threadably engaging the spindle, assembly and/or disassembly, particularly from the bottom of the pedestal, is difficult or impossible due to the spring loading so that disassembly from the top of the pedestal is normally required. This unduely complicates the pedestal structure, including the overall exterior appearance of the pedestal, and makes assembly and disassembly a complex and time consuming operation.
In addition, in the arrangement of the aforementioned British patent, the thread goes through the bearing housing and acts as an interrupted bearing surface for the spindle. This provides a wholly undesirable bearing arrangement, particularly during swiveling of the chair seat.
Another and very significant disadvantage of the known mechanisms, such as those identified above, is the relationship between the maximum height adjustment range versus the overall height of the mechanism. The known mechanisms have typically required a significantly large mechanism height, such as to provide the necessary spring size and deflection, in order to result in the mechanism having the desired range of height adjustment. Such mechanisms typically cannot be used in conjunction with a knee-type tilt control since such control itself typically occupies a significant vertical space beneath the chair seat and hence significantly reduces the vertical space available for the height-adjusting mechanism.
Accordingly, this invention relates to an improved height-adjusting mechanism for a spindle or pedestal-type chair, which mechanism is capable of providing a desirable height-adjusting function when the chair seat is unoccupied, which provides a maximum height adjusting range while minimizing the overall height of the mechanism, which creates a sufficient frictional engagement between the support tube and the chair spindle even when the chair seat is unoccupied as to prevent undesired height loss, which is readily and efficiently adjustable when desired, which is reasonably economical to manufacture, which can be readily disassembled and/or assembled from the lower end of the pedestal to simplify maintenance requirements, and which is believed to possess a high degree of reliability and durability.
In the improved height-adjusting mechanism of this invention, a non-threaded spindle as nonrotatably secured to the chair seat is rotatably telescopically supported within a support tube secured to the base. The spindle is urged upwardly (when the chair seat is unoccupied) by a spring which is confined between the spindle and a conical wedge disposed directly thereunder. The wedge is disposed for wedging engagement within a conical recess formed in a split nut, the latter being disposed in continuous externally threaded engagement with an internal thread formed on the support tube. A clutch member is secured to the spindle and clutchingly cooperates with the split nut. When the chair seat is occupied, the occupant weight acts through the spindle onto the wedge, whereby the nut is wedged radially outwardly into tight wedging engagement with the internal threads on the support tube so as to lock up the nut and prevent rotation thereof. The spindle can thus rotate about its vertical swivel axis so as to accommodate the desired swiveling by the chair occupant. In this occupied position, the clutch member is disengaged from the nut. When the chair is unoccupied, the spring urges the spindle upwardly and causes the clutch member to clutchingly engage the nut. This also relieves the occupant weight from the wedge so that the wedge is urged into engagement with the split nut solely by the spring. The split nut hence remains threadably engaged with the internally threaded support tube, which engagement is of significantly lesser magnitude since it is created solely by the spring force imposed on the wedge, whereby the nut can freely rotate within the support tube and will so rotate so as to cause height adjustment when the chair is manually rotated while unoccupied. However, due to the frictional engagement created between the nut and the internally threaded support tube, and the fact that the nut is nonrotatably coupled to the spindle, the chair seat will not free-wheel, but rather will be rotatable for height adjustment only when a deliberate rotating force is manually applied to the chair seat.
Other objects and purposes of the invention will be apparent to persons familiar with mechanisms of this general type upon reading the following specification and inspecting the accompanying drawings.